The role of a thrust reverser during the landing of an aircraft is to enhance the braking capacity of an aircraft by redirecting forward at least a part of the thrust generated by the turbojet engine. In this phase, the reverser obstructs the gas exhaust duct and directs the exhaust flow stream from the engine toward the front of the engine car, thus generating a counter-thrust which is added to the braking force of the aircraft wheels.
The means used for implementing this redirection of the flow stream varies depending on the type of reverser. However, in all cases, the structure of a reverser comprises mobile cowling sections moveable between, on the one hand, a deployed position in which they open up a passage in the engine car designed for the diverted flow stream and, on the other hand, a retracted position in which they close this passage. Furthermore, these mobile cowling sections can fulfill a diverter function or simply a function for activation of other diverter means.
In fin-array reverser systems, for example, the mobile cowling sections slide along rails in such a manner that, by sliding back during the opening phase, they uncover arrays of diverter fins disposed within the thickness of the engine car. A system of crank-rods connects this mobile cowling section to blocking doors which are deployed inside the exhaust channel and block the direct flow output. In door reversers, on the other hand, each mobile cowling section pivots so as to be made to block the flow stream and divert it and hence is active in this redirection.
Generally speaking, these mobile cowling sections are actuated by hydraulic or pneumatic jacks which require a high-pressure fluid transport system. This high-pressure fluid is conventionally obtained either by tapping off air from the turbojet engine in the case of a pneumatic system, or by taking fluid from the hydraulic circuit of the aircraft. Such systems require significant maintenance since the smallest leakage in the hydraulic or pneumatic system may be difficult to detect and risks having detrimental consequences both on the reversing and on the other parts of the engine car. Furthermore, owing to the reduced space available in the forward framework of the reverser, the installation and the protection of such a circuit are particularly difficult and cumbersome.
In order to overcome the various drawbacks associated with the pneumatic and hydraulic systems, the thrust reverser manufacturers have tried to replace them and, as far as possible, to equip their reversers with electromechanical actuators which are lighter and more reliable. Such a reverser is described in the document EP 0 843 089.
However, electromechanical actuators also exhibit several drawbacks which need to be resolved in order to take full advantage of the features they offer in terms of mass and volume gains.
In particular, under extreme temperature conditions, in other words for example for temperatures of around −40° C. or around 50° C., the torque delivered by the electric motor driving the electromechanical actuators can be insufficient for driving the latter and hence for enabling the mobile cowling sections to be moved.
Indeed, it has been observed that, under extreme temperature conditions, the electromechanical actuators require the electric motor driving the latter to deliver a torque greater than that delivered under normal temperature conditions in order to enable them to be driven.
Thus, under extreme temperature conditions, the operation of the thrust reverser may be compromised during the landing of an aircraft equipped with such a reverser.
One solution for overcoming this drawback would consist in adapting the electric motor in such a manner that it delivers a single torque high enough to allow the electromechanical actuators to be driven and hence the cowling sections of the reverser to be displaced under both normal temperature conditions and extreme temperature conditions.
However, for the electric motor to continuously deliver a high torque would lead to rapid wear of the electric motor and of the electromechanical actuators.
Moreover, the use of high currents has an impact on the reliability/lifetime of the control system power electronics.
The rapid wear of the electric motor and of the electromechanical actuators is all the more harmful as the delivery of a high torque is only necessary in a very few cases, since most of the time the control system is running under normal temperature conditions that do not require the delivery of such a torque.